Data model:It is a collection of concepts that can be used to descrie the structure of a database.

Database Schema:The description of database is called database schema.It is specified during database design andit is not change frequently.

Database state:The data in the database at a particular moment in time is called a database state or snapshot. It is also called the current set of occurrences or instances in the database.

Internal schema:It describes the physical storage structure of database and details of data storage and access paths for database.

Conceptual schema:It describes the structure of hole database.The conceptual schema hides the details of physical storage structures and concentrates on describing entities,data types, relationships, user operations, and constraints. 

External schema:It describes the part of the database that a particular user group is interested in and hides the rest of the database from thatuser group. 

Data independence:The capacity to change the schema at one level of a database system without having to change the schema at the next higher level.

DDL(Data Definition Language):To define the data and their relationship to other types of data and specifies conceptual schema only.

DML(Data Manipulation Language):The purpose of this languageis to retrieval,insert,delete and modification of data.

SDL(Storage Definition Language):To specify the internal schema and wwhere data in relevant table is stored.

VDL(View Definition Language):To specify user views and their mapping to conceptual schema and creates virtual tables.

Query language:It is a language used  that requests and retrives data from database and information systems by sending queries.

Host language:The language that is used for database application programming.It is may be a traditional programming language like C or COBOL.

Data sublanguage:It is used to define or manipulate the structure of a database systems.

Database utility:It manages the database systems like loading,backup,sorting files and handling data access by users and perfoming other functions.

Catalog:It is a collection of tables and views that contain information about database.

Client-server architecture:The client/server architecture was developed to deal with computing environments in which a large number of PCs, workstations, file servers,printers, database servers, Web servers, e-mail servers, and other software and equipment are connected via a network. The idea is to define specialized servers with specific functionalities. For example, it is possible to connect a number of PCs or small workstations as clients to a file server that maintains the files of the client machines. Another machine can be designated as a printer server by being connected to various printers; all print requests by the clients are forwarded to this machine. Web servers or e-mail servers also fall into the specialized server category.The resources provided by specialized servers can be accessed by many client machines. The client machines provide the user with the appropriate interfaces to utilize these servers, as well as with local processing power to run local applications.

Three tier and n-tier architecture:An intermediate layer between the client and the database server,This intermediate layer or middle tier is called the application server or the Webserver, depending on the application.It can also improve database security by checking a client’s credentials before forwarding a request to the database server. Clients contain user interfaces and Web browsers. The intermediate server accepts requests from the client, processes the request and sends database queries and commands to the database server, and then acts as a conduit for passing (partially) processed data from the database server to the clients, where it may be processed further and filtered to be presented to the users. Thus, the userinterface, application rules, and data access act as the three tiers.

It is possible to divide the layers between the user and the stored data further into finer components, thereby giving rise to n-tier architectures, where n may be four or five tiers. Typically, the business logic layer is divided into multiple layers. Besides distributing programming anddata throughout a network, n-tier applications afford the advantage that any onetier can run on an appropriate processor or operating system platform and can be handled independently. Vendors of ERP (enterprise resource planning) and CRM (customer relationship management) packages often use a middleware layer.